1. Field of the Invention
The present invention relates generally to a card cage used to support printed circuit cards particularly in telecommunications equipment such as optical network units and, more specifically, to a card cage that is readily manufacturable and convenient to assemble without the use of fasteners or tools.
2. Description of the Related Art
Telecommunications equipment of various types including optical network units, for example, have long been designed to use printed circuit cards to accomplish various electronic functions. Typically, the cards are supported in guides formed in a cage in side-by-side relation and establish electrical communication through suitable connectors mounted on a backplane assembly. The cage is often open to the front to permit the cards to be conveniently removed and replaced as desired.
The panels from which card cages are assembled have traditionally been fabricated most commonly from sheet metal such as aluminum, cold rolled steel and stainless steel. The metal is stamped and bent into the designed panel configurations then secured together by fasteners such as metal screws, nuts and bolt, rivets and spot welding. Assembly of such card cages, however, is relatively time consuming. A given fastening operation, for example, typically involves the requirement of several fasteners to construct a rigid cage assembly, which can be a relatively slow construction process.
Sheet metal has, in the past, been a material of choice for card cages because of its cost advantages over other suitable metals. However, sheet metal is susceptible to corrosion particularly when used in environments that are not climate controlled. Moreover, corrosion can be exacerbated by galvanic reactions between the card cage material and the fasteners, which typically are made of dissimilar metals. Coatings can be applied to protect the sheet metal from corrosion. However, such coatings may be damaged as fasteners are installed. On the other hand, if a protective coating is applied after the panels are assembled, it may be difficult to coat all surfaces of the panels.
It also will be appreciated that shipping of card cages is made more costly because of their relatively large bulk in comparison to their weight. Thus, it may be desirable in some applications to ship panels in an unassembled state for assembly at a local distribution center or at the site where the card cage will be installed. However, such off-site assembly may still not be a cost-effective alternative because of the time and expense of the assembly operation.
Accordingly, it is desirable to provide a card cage that is capable of assembly without the need for fasteners or tools of any kind. It is further desirable to provide such a card cage which is resistant to corrosive environments. Still further, it is desirable to provide such a card cage which is cost-effective to manufacture.